Corrugated cardboard boxes offer limited protection from shipping damage, but their low cost and ready availability make them attractive for many one-way shipments. Shocks due to rough handling of truck, rail and aircraft shipments impart kinetic energy to a box that may damage its contents unless the energy is effectively redistributed and dissipated by the box and internal packing materials, rather than being applied to the item(s) to be protected. Dissipation of imparted kinetic energy is typically manifest in localized flexing, crushing or disintegration of portions of box walls and/or packing materials. But the poor energy redistribution that is common in cardboard boxes means that some portions of box walls and packing materials may be overstressed and substantially destroyed while other portions remain undamaged. Unfortunately, failure of the overstressed portions may allow transmission of imparted energy to contents that the box was intended to protect.
Even if the box contents arrive at their destination undamaged, the box and/or its internal packing may be sufficiently degraded to prevent their use for returning defective goods for repair. Attempts to reduce the incidence and severity of damage to both the box and its contents have resulted in design changes applicable to both corrugated boxes and their internal packing materials. See, for example, U.S. Pat. No. 5,417,342, incorporated herein by reference.
When the upper and lower portions of a box according to the '342 patent were assembled, the box assembly had four corrugated layers on each of its four side walls, as well as in the top and bottom closure. But the four layers in the top and bottom closures were interrupted by flaps so that there was no continuous corrugated layer across either the top or bottom of the box assembly. A modification of the '342 box design introduced circa 2001 substituted a single continuous corrugated top wall layer for the top flap closure and, analogously, also substituted a single continuous corrugated bottom wall layer for the bottom flap closure. By eliminating the top and bottom flap closures, a possible failure mode of the '342 box design (i.e., failure caused by the flaps springing open due to shipping shock) was also eliminated. Additionally, the modified box was easier to construct than the original '342 box design.
But field experience showed that the disparity between side wall thickness (i.e., four corrugated layers) and top and bottom wall thickness (i.e., a single corrugated layer) made the modified box especially susceptible to shipping shocks applied to either the top or bottom. This susceptibility was addressed through use of thick internal foam pads across the top and bottom. While effective for reducing shock damage to box contents, these thick foam pads added significantly to the box outer dimensions and thus limited overall packing density achievable with the modified box.
Other corrugated box suppliers addressed the problem of foreshortened service life of corrugated boxes with designs featuring strengthened box walls (e.g., walls having thicker and/or stronger varieties of corrugated material in multiple layers). But such changes alone can actually increase susceptibility to shipping damage to box contents by reducing the box's capacity for energy redistribution and dissipation. If at least a portion of the energy imparted to a box is not redistributed and dissipated by the box itself, it may be transmitted in a damaging localized form to the packing material. And unless the packing material is particularly effective, significant energy may in turn be transmitted to (and may damage) the item(s) intended to be protected. Thus, the use of more robust boxes necessarily increases the need for effective energy redistribution to allow generalized dissipation by the internal packing material without permanent damage. This requirement is especially prominent for boxes comprising relatively strong materials such as corrugated polypropylene.
Consequently, corrugated polypropylene boxes intended for extensive re-use are provided with relatively thick and resilient linings (frequently comprising plastic and/or rubber foam) that conform to the shape of items to be shipped. Such resilient linings can be made relatively light and yet are effective for protecting box contents through dissipation of absorbed kinetic energy. But the thick, soft linings occupy considerable space, while they are less effective for redistributing localized shock energy than more rigid structures. This means that a box suitable for shipping a given item is often relatively large compared to the item to be shipped. Aggregations of such boxes for shipment (as on pallets) are then more likely to be limited by their total volume than by their weight. Transport vehicles and aircraft carrying such shipments operate relatively inefficiently because the overall density of shipments is less than optimal.
If, on the other hand, overall shipment density could be increased to optimal levels at reasonable cost without sacrifice of protection for the goods shipped, the result would be the desirable combination of lower transportation costs and less shipping damage. One approach to achieving this combination lies in raising the efficiency of energy redistribution and dissipation by the system that comprises the corrugated box, the packing materials within, and the item(s) being shipped.